Latest Cretaceous basin formation within the Salinian terrane of west-central California

Abstract

Sedimentologic details provide new information about the controversial Late Cretaceous-early Tertiary history of the Salinian terrane, a displaced crustal block located in the California Coast Ranges. The preserved Upper Cretaceous strata were deposited as part of a fan-delta-submarine-fan system along the margin of a topographically steep basin bounded by normal faults. Coarse-grained sediments, derived from local basement rocks and volcanic rocks of a mature magmatic arc, were shed southward from a basement high north of the basin. Sediment compositions suggest connections to the southwestern Mojave Desert region. Paleomagnetic data collected from the central Salinian terrane indicate minimal northward transport relative to cratonal North America and support the hypothesis of an origin in southern California, rather than in southern Mexico/Central America. The Upper Cretaceous Salinian basin may have formed as an east-west-trending fore-arc graben that partitioned the Cordilleran arc into northern and southern segments, like the Sunda Strait, an extensional basin in Indonesia. Sunda Strait is a transition zone between Java, where the oceanic plate is subducting at right angles to the magmatic arc, and Sumatra, where the oceanic plate is subducting at an oblique angle. Like the right-lateral Central fault in Sumatra, right-lateral faults in the Sierra Nevada accommodated oblique subduction and facilitated extension where the subducting angle changed. The Late Cretaceous structures that accommodated extension in the Salinian terrane are not visible because of subsequent Cenozoic tectonism, which has slivered the terrane from a compact block into pieces that now extend from the Transverse Ranges to coastal locations north of San Francisco.